Evaluation of closed-form analytical models to calculate conductivity in a fine sand

• Published in: Soil Science Society of America journal Vol. 49; no. 1; pp. 12 - 19
• Main Authors: Stephens, D.B, Rehfeld, K.R
• Format: Journal Article
• Language: English
• Published: Madison, WI Soil Science Society of America 01-01-1985
• Subjects: Agronomy. Soil science and plant productions; ARENA; Biological and medical sciences; Biometrics, statistics, experimental designs, modeling, agricultural computer applications; CARACT MORFOLOGICAS (SUELOS); CONDUCTIVITY; CONTENIDO DE AGUA EN EL SUELO; Fundamental and applied biological sciences. Psychology; Generalities. Biometrics, experimentation. Remote sensing; Physical properties; Physics, chemistry, biochemistry and biology of agricultural and forest soils; SABLE; SAND; SOIL MORPHOLOGICAL FEATURES; Soil science; SOIL WATER CONTENT; TENEUR EN EAU DU SOL; TRAIT MORPHOLOGIQUE DU SOL; Water and solute dynamics; Water; Soil; Hydraulic conductivity; Models; Sand
• ISSN: 0361-5995; 1435-0661
• DOI: 10.2136/sssaj1985.03615995004900010002x

The soil‐water characteristic curve, θ—ψ, was determined for an undisturbed core of fine sand over a range of negative pressure heads observed in the field, 0 to 150 cm, below about the 30 cm depth. These data were used to predict relative hydraulic conductivity in a computer code of closed‐form analytical solutions developed by van Genuchten for the theoretical models of Burdine and Mualem. The equations to predict conductivity are based upon two parameters fit to observed θ—ψ data by a non‐linear least squares procedure. The two parameters are influenced by the choice of residual water content, θr, and unsaturated water content, θs. If θr is unknown, it is estimated in the program from observed data. A sensitivity analysis was performed to evaluate the reliability of the models. For this soil, calculated conductivities appear to be sensitive to θr. If θ—ψ data are available over only a limited range, or if θs is too large, model‐predicted θr‐values may be near zero, whereas θ at large ψ may actually be about 0.06 to 0.08 cm3/cm3. Predicted conductivities may differ by more than one order of magnitude at about ψ = 150 cm, depending on the choice of θr.